In an image forming apparatus applying an electrophotographic system, an electrophotographic photoreceptor having deposition layers including a photosensitive layer is mounted on an outer peripheral surface of a cylindrical base formed of, for example, aluminum. As such electrophotographic photoreceptor, there are a positive-charge electrophotographic photoreceptor in which surface charges are positive and a negative-charge electrophotographic photoreceptor in which surface charges are negative. Normally, the positive-charge electrophotographic photoreceptor is configured by forming deposition layers including a charge injection blocking layer, a photoconductive layer and a surface layer in this order on the cylindrical base, and the negative-charge electrophotographic photoreceptor is configured by forming deposition layers including the photoconductive layer, the charge injection blocking layer and the surface layer in this order on the cylindrical base. That is, in the negative-charge electrophotographic photoreceptor, the charge injection blocking layer exists on the photoconductive layer, which differs from the positive-charge electrophotographic photoreceptor. Examples of such a negative-charge electrophotographic photoreceptor include a photoreceptor disclosed in Japanese unexamined Patent Publication JP-A 7-120952 (1995).
However, there is a problem that image characteristics, particularly the image contrast is reduced though an electrostatic property is improved.
The invention has been made in view of the above problems, and an object thereof is to provide a negative-charge electrophotographic photoreceptor capable of maintaining the image characteristics to be relatively higher while improving the electrostatic property.